Rule Request: Unnecessary closure used in stored property default value with single expression

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

(I feel like this one is a bit challenging to search for, so my apologies if there's already an issue or if it's already implemented)

New rule request

Possible rule identifier: unnecessary_property_closure (open to suggestions)

When a stored property's default value requires some customization/setup, it's often useful to use a closure as follows:

let closeButton: UIButton = {
    let button = UIButton()
    button.setImage(UIImage(named: "close"), for: .normal)
    return button
}()

But when that setup is done using a single expression, the closure is unnecessary:

// Unnecessary closure - should trigger a warning
let closeButton: UIButton = {
    return UIButton() 
}()

// More concise
let closeButton = UIButton()

This new rule should warn when using such an unnecessary closure with a single expression. I don't feel strongly one way or another about whether this should be enabled by default. This rule could probably support autocorrect as well.

Start by comparing the two stored-property examples in the issue and define the exact single-expression closure cases the rule should report. Decide whether the rule is enabled by default and whether autocorrection is in scope; done means the requested unnecessary closure is detected without flagging the multi-statement setup example.